Homebrew PCBs

Simon Gornall wrote:
> The SSR's will arrive in January next year, so perhaps I'll have a
> chance to work on it then.
> Apart from the chemistry, you're still looking at the high-hundreds
> for a reverse-pulse-plating machine if you DIY it. I can't see the
> price being much more "affordable" than that if it's sold
> commercially.

Hi, Which SSR's are you using? Can they do 0.5ms pulses? Or operate at
1V or less? The turn on time and the minimum voltage to operate seems
out off necessary range. Most the datasheets i shaw for 10-50A DC SSR's
had 10ms maximum turn on time, and 3V minimum required voltage to
operate. There was some at sub-0.5ms turn on but for 1A or so. Just
wondering did you checked if the SSR's you ordered fit the purpose?

Pulse plating documentation refers the value of a good square wave so
fast turn on/off is recommended. Mine idea of a plating driver was
started by a crazy wish of a electronically regenerated etchant, was to
test chemistries than could fit this desire, were very high current
densities define the efficiency. Fitting both purposes became not so
simple.
But any person with it's feet on the ground would just need 2 MOSFETs, 2
PSUs, a dual driver and a MCU with PWM to archive it. STP80NF55 (one for
direct other for reverse) and any dual 10V 2A driver gives you around
100ns for less money than one SSR.



It helps me some brainstorm-loud-thinking to set some ideas from
questions raised on this old thread, so...

Trying to understand the copper plating required voltage: Half Cell
potential for copper is +0.34V, if i understand the thing right, using
both copper anode and cathode there is no minimum required potencial for
deposition. According to graphics from cyclic voltametric stripping
(CVS) tests used to mesure additive behavior/content, copper start
plating right at 0.0V+, it start increasing faster at 0.2~0.3V and this
curve can be slower according to additives use. The current increase up
to a standing current point, that stands until the water electrolysis
voltage. 
I don't really remember the precise value on the bath i had access to,
was something about 2V in the power supply voltmeter. But wires,
connections and resistive titanium holders will always increase this
value on the power supply stage. Before i tried to get a simple answer
to this so i could choose PSU voltage, and got ~0.7 minimum 3V best, and
was wrong, i don't find any such reference in any documentation now, and
a 5V PSU may only fit if enough resistance exists between PSU and
plating cell , or by adding one power resistor in the circuit.
Finding water electrolysis voltage value is not easy without having good
chemistry skills, i think it's 1.23V, but in a sulfuric bath should be
2.05V but don't know for sure.
According to real descriptions shared on this discussion group: One
platter and is bought palladium chemistry and additives, say 0.6V for
plating voltage. He describes for PSU a 5V toroidal transformer and a
light dimmer on AC side for regulation. He later added series rectifier
diodes on the DC side to increase the minimum voltage about 3V so the
light dimmer work as useful controller. Other platter with is fully
homebrew carbon black chemistry describes using a 5V output from an ATX
PSU with steel wire as power resistor, using  a alligator clip to choose
desired current position. He reports 0.7V on the bath 1.6V at PSU with
macdermind brightener.
Seems to be possible to conclude that plating will occur under 1V and
with total connections and wires resistance should be required 2~3V on
the PSU. The use of one 5V PSU and a resistor can help the current
control. 

ATX PSUs are a easy choice. I would also wish that adjustable voltage
and current could be done for cheap at the PSU directly. I learned that
some PSUs from meanwell use DC side simple PWM controllers, with a
current sensor. On such, a resistor replacement by pots would be enough
to slightly vary voltage/current. One attempt on a 5V 25A PSU didn't
fully work, (but at least didn't ended in smoke like other times i tried
to hack switched mode PSUs :D) IIRC i made the thing going down from 5V
to 2.5V as expected but only goes back up to 3V... I couldn't test the
current control because with a 20A multimeter directly connected, the
PSU don't even power on, and trying with a steel welding rod as a 1ohm
power resistor it didn't turn on either. I have to get something for
test load, and the voltage modification isn't convenient done, at the
store they didn't had the needed potentiometer values and i ended
modifying other resistor values to fit. I have to try again. 

About the pcb plating, there are plenty people in this group which do it
themselves (either by commercial/homebrew machines/chemistries), none of
them, by what was shared, seem to bother with reverse pulses. It's an
obvious good thing, but not an simpler/complete solution. 
Currents and pulse times vary with chemistries, and such vary with
desired throwing power and aspect ratios. You can find very
different&confusing copper/acid ratios between chemistries; high aspect
ratio tend to have more acid and less copper; faster high current
densities have more copper and less acid; reverse pulse chemistries
prefer less acid more copper and highly suppressing current additives
(bigger potencial variance for current adjust). 
Using additives can be PITA in medium term for a non chemistry knowledge
guy, like i have experienced. Worst, if using this less often you end
not having all the technical stuff present in your mind, ending in
mistakes and boring repeated readings, like myself.
I would like to replace leveler with reverse pulses and brightener with
filtration for my use, but further reading tells me its not quit as
first thought, if it works will be like lottery. There is a supplier
that promotes additives free, reverse pulse plating chemistry, but their
patents don't disclosure much... except it don't use brightener or lever
but use catalyst and suppressor (which are not consumed like leveler and
brightener and are considered initial setup).

Catalyst and suppressor additives are simple chemicals that i got, other
3 organic compounds used as leveler can afterall be found as dye or pH
indicator in pure chemical too, but its useless without brightener
(Cl-PEG-SPS based system). Brightener is impossible to get as pure
chemical in low quantities, only from plating supplies as a set. But for
both leveler and brightener were once used thiourea (i also have it)
with the downside of lowering plated copper conductivity.
In the day i finally manage to get all the chemicals for the activation
chemistry i most probably will use a very simple DC plating setup. Too
much variables is a bad start. 

About the graphite drilling activation, i managed to find a old post
from the same author of
drilling-above-graphite-powder-mechanical-activation about his success
rate, were he says better than 1:200 hole failure rate! (but with
previous descriptions of 50% failure on <0.6mm holes and a initial
success report of 10% failure rates with 1mm holes). So considering
0.8mm vias and a learning curve seems a fair good system.

I also managed to find a number for the carbon black bath life. Graphite
chemistry can reach one day life, it suffers from CO2 absorption. Carbon
black as a problem of losing (???) oxygen, but i never saw bath life
quantified. The person says that expect 1-2 years life with his homebrew
chemistry. I was guessing much less, and am still curious about how the
real life ended to be... 

About palladium and carbon black. The plating machine i had access to,
had quiet some history about misuse of the chemistry. Loosing the
palladium bath by drag-on from previous bath because insufficient
rising, plated copper peeling off because not yet hot salt remover use,
and so. Not only is a bit sensitive but one have to use it rigorously.
And people tend to make mistakes with it, i was told that similar
machines were without use because owners ended spending more money with
it that if ordering the PCBs from a boardhouse. 
Besides the drying and repeat steps of a carbon black chemistry, if one
could mix it from things possible to dump without worrying about money
spent or environmental issues, if one damage it, it's always easy to
start over.

Good year,
Simao